SHAPE-MEMORY ALLOYS AS NEW MATERIALS FOR ASEISMIC ISOLATION

New results are presented in the area of hysteretic modeling and experimental characterization of shape memory alloys (SMAs). A stress-induced micromechanical phase transition occurs in SMAs that causes inelastic deformation and gives rise to a large energy-absorbing capacity. Because it is possible to achieve large hysteretic deformation in SMAs without incurring plastic deformation, SMAs have potential for use in earthquake-engineering passive damping schemes. In order to represent such energy-absorbing behavior, an existing one-dimensional model of hysteresis is modified to include the macroscopic characteristics of SMAs. Also, the results of cyclic material-characterization tests applied to a nickel-titanium SMA known as Nitinol are presented. Hysteretic behavior closely resembling that of the superelastic material was obtained in the laboratory for cyclic strain levels up to 4.5%. The model of SMA behavior is also compared to the cyclic responses of Nitinol.